Oocytes of different species may be classified due to the amount and disposition of yolk inclusions.

Oocytes
of different species may be classified due to the amount and disposition of
yolk inclusions.



1. Alecytal ones have no inclusions (insects).



2. Oligolecytal cells contain moderate yolk
inclusions. In primary isolecytal oocytes nuclei lie in the center of cells, in secondary isolecytal (female)
nuclei are disposed eccentrically.



3. Fish and birds have polylecytal oocytes with great volume of yolk.
According to location of this inclusions there are centrolecital and telolecital oocytes.














Biologic significance of oocyte in the
fertilization process.



1.
They give half of a necessary amount
of chromosomes.



2.
Supply the nutrition of embryo.



3.
Protection of embryo at the early
stages of development.










Fertilization is the
first stage of embryogenesis, the process by which the male and female gametes
fuse and result in zygote appearance.



The biological
significance of fertilization are
the next:



1.
The restorations of the full chromosomal set.



2.
Determination of the embryo sex.



3.
Initiation of a cleavage.







In female this process takes place
in the ampullar portion of the Fallopian (uterine) tube. Some specific
processes occur in the course of fertilization, which includes distant and contact stages.



Distant stage of
fertilization means special interaction of ovum (in uterine tube) and spermatozoa,
which enter female vagina. Contact stage begins after their meeting in
uterine tube.



Distant stage of fertilization
includes next processes: capacitation and taxis of spermatozoa. This stage
begins with special activation of spermatozoa and continues with their active
movement forward the ovum). Spermatozoa in vagina are not active. In the female
genital way they have to be activated.